1. Field of the Invention
This invention relates to a printer, and more particularly to a printer provided with an ink remainder detecting means.
2. Description of the Related Art
In a printer, an ink container is generally mounted to be removable from the printer body, and when the ink in the ink container is consumed, the ink container is replaced with a new refill (a disposable type) or the ink container is removed from the printer body, refilled with ink and then returned to the printer body (a reusable type).
Which ever type is employed, it is necessary to watch the remainder of ink in the ink container, or the ink can suddenly run out to force the printer to be stopped until the ink container is replaced with anew refill or the ink container is refilled with ink. That the time efficiency is high is a strong point of a printer such as a stencil printer. However when the ink suddenly runs out to force the printer to be stopped until the ink container is replaced with a new refill or the ink container is refilled with ink, such a strong point of the printer is hurt. Accordingly, it is necessary that the ink is about to be exhausted is recognized at least immediately before the ink actually runs out.
This problem can be overcome in the simplest way by the user visually watching the remainder of ink. However since the ink container is generally placed deep in the printer, the user must check the remainder of ink by taking out the ink container and opening the cap with the printer stopped. If the ink container is of transparent or semitransparent material, the user can check the remainder of ink with the cap kept on. However these actions are troublesome to the user. Accordingly, systems for detecting that the remainder of ink in the ink container becomes small have been proposed or have been put into practice.
For example, in a first system disclosed, for instance, in Japanese Unexamined Patent Publication No. 7 (1995)-61739, ink is sucked out from the ink container and supplied to the printing drum by an ink pump, and when no ink is sucked out from the ink container in response to operation of the ink pump, it is determined that there hardly remains ink in the ink container.
In a second system disclosed, for instance, in Japanese Unexamined Patent Publication No. 6(1994)-199371, a light emitting/receiving optics is provided on the ink container to emit light toward an inner cap for scraping down ink and to receive reflected light from the inner cap, and the remainder of ink in the ink container is determined on the basis of the amount of reflected light which represents the position of the inner cap.
Third, there has been proposed a system in which a plurality of light emitters are positioned on one side of a semitransparent ink container at different levels with a plurality of light receivers positioned on opposite side of the ink container to be opposed to the respective light emitters so that when ink exists between a combination of the light emitter and the light receiver, light emitted from the light emitted cannot be received by the light receiver. The remainder of ink in the ink container can be detected on the basis of which light receiver receives light and which light receiver does not receive light. In this system, the remainder of ink can be detected in a plurality of stages, e.g., the ink container is full, the remainder of ink is not smaller than a predetermined amount, or the remainder of ink is smaller than the predetermined amount.
The first system is disadvantageous in that though it can detect whether or not ink remains in the ink container, it cannot detect the amount of the remainder of ink in the ink container, and accordingly, the user cannot obtain information on the remainder of ink until the ink runs out, which does not permit the user to prepare in advance against ink running out.
Further, though the second system can theoretically detect the remainder of ink continuously, actually it is very difficult to accurately detect the remainder of ink. That is, the light projected onto the inner cap is reflected not only by the inner cap but also by various surfaces such as inner wall surfaces of the ink container, and the inner cap is not strictly held horizontal. Accordingly, noise is often generated in the reflected light, which deteriorates accuracy in detecting the remainder of ink.
Further, when light emitters are positioned on one side of a semitransparent ink container and light receivers positioned are disposed on opposite side of the ink container to be opposed to the respective light emitters, the light receivers receive light after it travels through the wall of the ink container twice, which results in that the light receivers can receive only a very small amount of light and accuracy in detecting the remainder of ink is deteriorated.
In view of the foregoing observations and description, the primary object of the present invention is to provide a printer in which the remainder of ink can be more accurately detected before ink actually runs out with a simple method and structure.
In accordance with the present invention, there is provided a printer comprising a printing mechanism which prints on printing media with ink, and an ink container which supplies ink to the printing mechanism and comprises a cylinder having a side wall formed of transparent or semitransparent material and provided with an ink discharge port in a front end face thereof, a piston received in the cylinder to be slidable along the sidewall of the cylinder in the longitudinal direction thereof, and ink between the piston and the front end face in the cylinder, wherein the improvement comprises
a light projecting means which projects light onto the side wall of the cylinder in a predetermined position in the longitudinal direction of the cylinder,
a photodetector which is positioned near a rear end face of the cylinder to be adapted to receive the light projected by the light projecting means and passing through the side wall of the cylinder only once, and outputs an electric signal upon receipt of light, and
an ink remainder detecting means which detects the remainder of ink in the ink container on the basis of the electric signal output from the photodetector.
The xe2x80x9ctransparent or semitransparentxe2x80x9d material of the side wall of the cylinder is a material permeable to the light projected by the light projecting means to such an extent that the photodetector can detect the light emitted from the light projecting means through the side wall of the cylinder.
The ink container may be of a type which is fixed to the printer body and is refilled with ink when the ink is consumed, or a type which is removably mounted to the printer body and is replaced by a new refill (i.e., a new ink container filled with ink) when the ink is consumed, or a type which is removably mounted to the printer body, removed from the printer body, refilled with ink and then returned to the printer body when the ink is consumed.
It is preferred that the light projecting means comprises a plurality of light emitting elements which are provided to project light beams onto the side wall of the cylinder in a plurality of different positions as viewed in the longitudinal direction of the cylinder and are turned on in different manners by position, and
the ink remainder detecting means detects the remainder of ink in the ink container on the basis of change in the electric signal output from the photodetector.
For example, the light emitting elements may be momentarily turned on in sequence by position, or the light emitting elements may be turned on at different timings by position or the light emitting elements may be turned off at different timings by position.
Also, it is possible that the light projecting means comprises a plurality of light emitting elements which are provided to project light beams onto the side wall of the cylinder in a plurality of different positions as viewed in the longitudinal direction of the cylinder and are simultaneously turned on, and
the ink remainder detecting means detects the remainder of ink in the ink container on the basis of the level of the electric signal output from the photodetector.
It is preferred that a plurality of light emitting elements be provided to project light beams onto the side wall of the cylinder in different circumferential positions in each longitudinal position.
Since ink is generally impermeable to light, when the light projecting means projects light onto the side wall of the cylinder in a position where ink still exists, no or very little light is received by the photodetector, and accordingly the output of the photodetector is 0 or substantially 0. Whereas, when the light projecting means projects light onto the side wall of the cylinder in a position where ink does not exist, a major part of the light projected by the light projecting means is received by the photodetector, and accordingly the output of the photodetector is at a high level.
In one very simple embodiment of the present invention, a single light emitting element is provided to project a light beam onto the side wall of the cylinder in a single longitudinal position.
In this case, if ink still exists in the longitudinal position of the cylinder in which the light beam is projected, light emitted by the light emitting element hardly reaches the photodetector whereas if no ink remains in the longitudinal position of the cylinder in which the light beam is projected, light emitted by almost all the light emitting element reaches the photodetector. Accordingly, it may be determined whether the ink remains up to the position on the basis of the output of the photodetector.
Further, it is possible to provide a plurality of light emitting elements to project light beams onto the side wall of the cylinder in a plurality of different longitudinal positions. In this case, the remainder of ink in the ink container can be detected in a plurality of stages when the photodetector is effective enough to detect the difference in the amount of light which changes with the number of light emitting elements the light from which is cut by ink. Even if the photodetector is not so sensitive, the remainder of ink in the ink container can be detected in a plurality of stages by turning on the light emitting elements in different manners by position.
For example, by turning on the light emitting elements are momentarily turned on in sequence by position while watching whether the photodetector receives light, the light from which is cut by ink can be detected, whereby the remainder of ink in the ink container can be detected in a plurality of stages.
Further, so long as the photodetector can sense change in the amount of light when one of the light emitting elements are turned on in addition or when one of the light emitting elements which have been on is turned off, the remainder of ink in the ink container can be detected in a plurality of stages by turning on or off the plurality of light emitting elements at different timings.
Depending on the kind of the light emitting elements, e.g., in the case of the LED, light can be emitted in higher intensity when the elements are turned on in a pulse-like fashion than when the elements are continuously operated, which contributes to increase in detecting accuracy.
When a plurality of light emitting elements are provided to project light beams onto the side wall of the cylinder in different circumferential positions in each longitudinal position, the remainder of ink can be accurately detected even if the inner surface of the cylinder is stained by ink, or the ink is consumed in different amounts in a circumferential direction of the cylinder. In this case, it is preferred that a larger number light emitting elements be provided for a longitudinal position existence of ink in which is to be more accurately detected, e.g., the position corresponding to zero remainder.
The present invention can be applied to existing printers as they are so long as the side wall of the cylinder of the ink container is permeable to light.
When the ink remainder is thus detected, for instance, deterioration in time efficiency due to ink suddenly running out during printing can be prevented.
Further, since light emitted from the light projecting means passes through the side wall of the cylinder only once before received by the photodetector, the light is not weakened, whereby the remainder of the ink in the ink container can be more surely detected.